The criminal trial for Paul Manafort, President Trump’s former campaign manager, will likely start this fall, according to a federal judge, and could cast a shadow over the upcoming midterm elections.

Mr. Manafort and his business partner Richard Gates face charges stemming from special counsel Robert Mueller’s probe into allegations of Russian meddling in the 2016 presidential election. Charges include conspiracy against the United States, conspiracy to launder money and failing to register as foreign agents for political work they did for a pro-Russia Ukrainian political party. Prosecutors were reportedly pushing for a May start to the trial.

On Tuesday at the U.S. District Court for the District of Columbia, however, Judge Amy Berman Jackson said the Manafort-Gates trial might not start until September or October.

“I’m not exactly sure when the trial date might be,” Judge Berman Jackson said during an hourlong status conference, according to reports.

Mr. Manafort and Mr. Gates are under house arrest. Part of the delay stems from the time Mr. Manafort’s and Mr. Gates’ attorneys need to process thousands of pages of material they have been given by Department of Justice lawyers for Mr. Mueller related to the case, reports said.

Judge Berman Jackson also cited a separate, civil lawsuit Mr. Manafort filed against Mr. Mueller and the DOJ earlier this month as reason for the delay.

That lawsuit, considered unusual because it was filed in civil court, is against Mr. Mueller, Deputy Attorney General Rod Rosenstein and the DOJ. It accuses the parties of legal overreach, arguing that they overstepped their authority by charging Mr. Manafort with crimes that predated allegations of Russian meddling in the 2016 presidential election.

According to reports on Tuesday, DOJ Prosecutor Andrew Weissmann told the judge he would file a motion to dismiss the lawsuit by Feb. 2 on the grounds that the issues it raises should be addressed in Mr. Manafort’s criminal case — as opposed to a separate civil court proceeding.

On Tuesday, Judge Berman Jackson declined to express an opinion on Mr. Manafort’s civil case, other than to say it “is a rather unique situation.”

She also gave Mr. Manafort and Mr. Gates until Feb. 23 to file motions addressing possible defects in the criminal case. The next status conference in the case, according to reports, will occur on Feb. 14.

Republicans are defending their majorities in the House and Senate in November’s midterm elections. Pundits noted that extensive media coverage of a Manafort money laundering trial running alongside the elections could negatively impact the GOP’s bid to hold its majorities.